Stephenson 2

Stephenson 2
Observation data (J2000 epoch)
Constellation Scutum
Right ascension 18h 39m 20s[1]
Declination −06° 01′ 42″[1]
Distance ~20 kly (~6 kpc[2])
Apparent magnitude (V) not visible[2]
Apparent dimensions (V) <7′[2]
Physical characteristics
Mass 3–5 × 104[2] M☉
Radius ~4 pc[2]
Estimated age 14–20 my[2]
Other designations RSGC2

Stephenson 2 also known as RSGC2 is a young massive open cluster belonging to the Milky Way galaxy. It was discovered in 1990 in the data obtained by a deep infrared survey.[2][3] The only members of the cluster that are currently identified are 26 red supergiants—young massive stars undergoing helium burning in their cores. The cluster is located in the constellation Scutum at the distance of about 6 kpc from the Sun. It is likely situated at the intersection of the northern end of the Long Bar of the Milky Way and the inner portion of the Scutum–Centaurus Arm—one of the two major spiral arms.[2]

A more recent study has identified around 80 red supergiants in the line of sight of Stephenson 2, approximately 40 of them with radial velocities consistent with being cluster members. However these stars are spread over a wider area than a typical cluster, indicating an extended stellar association similar to that found around the nearby cluster RSGC3.[4]

The age of Stephenson 2 is estimated at 14–20 million years. The observed red supergiants with the mass of about 12–16 solar masses are type II supernova progenitors. The cluster is heavily obscured and have not been detected in the visible light. It lies close to other groupings of red super giants known as RSGC1, RSGC3 and Alicante 8.[5] The mass of the open cluster is estimated at 30–50 thousand solar masses,[2] which makes it the second most massive open cluster in the Galaxy.

References

  1. ↑ 1.0 1.1 "SIMBAD Astronomical Database". Results for RSGC2. Retrieved 2011-01-09.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Davies, B.; Figer, D. F.; Kudritzki, R. P.; MacKenty, J.; Najarro, F.; Herrero, A. (2007). "A Massive Cluster of Red Supergiants at the Base of the Scutum‐Crux Arm" (pdf). The Astrophysical Journal 671: 781. arXiv:0708.0821. Bibcode:2007ApJ...671..781D. doi:10.1086/522224.
  3. ↑ Stephenson, C. B. (1990). "A possible new and very remote galactic cluster". The Astronomical Journal 99: 1867. Bibcode:1990AJ.....99.1867S. doi:10.1086/115464.
  4. ↑ Negueruela, I.; Marco, A.; González-Fernández, C.; Jiménez-Esteban, F.; Clark, J. S.; Garcia, M.; Solano, E. (2012). "Red supergiants around the obscured open cluster Stephenson 2". Astronomy & Astrophysics 547: A15. arXiv:1208.3282. Bibcode:2012A&A...547A..15N. doi:10.1051/0004-6361/201219540.
  5. ↑ Negueruela, I.; González-Fernández, C.; Marco, A.; Clark, J. S.; Martínez-Núñez, S. (2010). "Another cluster of red supergiants close to RSGC1". Astronomy and Astrophysics 513: A74. arXiv:1002.1823. Bibcode:2010A&A...513A..74N. doi:10.1051/0004-6361/200913373.